KR19990029845A - Method of inhibiting polymerization during distillation of vinyl aromatics - Google Patents

Abstract

The present invention is directed to adding a nitroso compound such as N-nitroso-N, N'-di-3-pentyl-p-phenylenediamine to a vinyl aromatic compound, thereby diluting the vinyl aromatic compound during the distillation of the vinyl aromatic compound. It relates to a method of inhibiting polymerization.

Description

Method of inhibiting polymerization during distillation of vinyl aromatics

The present invention relates to the polymerization of the compound during the distillation of a vinyl aromatic compound such as styrene to a nitroso compound such as N-nitroso-N, N'-di-3-pentyl-p-phenylene to the vinyl aromatic compound. It relates to a method of suppressing by adding diamine. Styrene is one of the few vinyl aromatic compounds of considerable industrial value. Polymerization of styrene results in polystyrene which is very transparent, easily colored and easily processed into many plastic products. The efficiency of the polymerization process depends on the purity of the monomer that is the starting material. Since the procedure for preparing styrene and other vinyl aromatic compounds will contain various reaction products including benzene, toluene and the like, the mixture is distilled off to separate these undesirable contaminants. Unfortunately, temperatures of 90 to 150 ° C., which are the temperatures required for distillation, lead to the polymerization of vinyl aromatic compounds. In order to minimize or prevent the polymerization of vinyl aromatic monomers, it is common to add polymerization inhibitors to the distillation mixture.

Various compounds are known in the art for polymerization inhibition. US Patent No. 4,050,993 describes the use of N, N-nitroso-methylaniline as a polymerization inhibitor. US Patent No. 3,988,212 describes the use of N-nitrosodiphenyl amines with dinitro-o-cresol. US Patent No. 4,013,580 describes the use of N-nitrosoaniline derivatives. US Pat. No. 4,341,600 describes the use of a mixture of dinitro-p-cresol and N-nitroso-diphenyl amine. US Pat. No. 4,654,451 describes alkyl substituted p-nitroso phenols with p-nitroso phenyl. U.S. Patent No. 5,034,156 describes N-nitrosophenyl-hydroxylamine and hydroquinone monomethyl ether. U.S. Patent 5,396,004 describes phenylene-diamine compounds and hydroxyalkylhydroxyl-amine compounds. U.S. Patent 5,254,760 describes 1-oxy-2,2,6,6-tetramethylpiperidine and aromatic nitro compounds. US Patent No. 4,929,778 describes phenylenediamine compounds and hindered phenolic compounds. U.S. Patent 5,312,952 describes the reaction products of sulfuric acid and nitric acid with C ₉ -C ₂₀ alkyl phenols, and optionally with aryl-substituted phenylenediamine or alkyl-substituted phenylenediamine. International Publication No. 9503263 describes 3,5-di-tert-butyl-4-hydroxy-N, N-dimethyl benzyl amines. EP-A-697386 describes 4-acetylamino-2,2,6,6-tetramethyl piperidine N-oxyl with 4-nitroso phenol. Japanese Patent Laid-Open Publication No. 0701010 describes phosphite compounds, nitrosoamine compounds or phenol compounds. Japanese Patent Laid-Open No. 05310815 describes ammonium salts of N-nitrosophenyl hydroxylamine. Japanese Patent Laid-Open No. 03149205 describes nitrosophenol and dicyclohexyl ammonium nitrate. Japanese Patent Laid-Open No. 1226858 describes the use of substituted nitrosobenzenes. US Pat. No. 4,967,027 describes p-nitroso phenol and pt-butyl catechol. Japanese Patent Laid-Open No. 59029624 describes the use of N-nitroso compounds (e.g., N-nitroso-diphenylamine) and catechol (e.g., pt-butylcatechol).

Accordingly, it is an object of the present invention to provide a method for inhibiting polymerization using a compound which is effective for inhibiting polymerization of a vinyl aromatic compound as compared to a conventional polymerization inhibitor.

In contrast to conventional compounds, generally a series of compounds has been found in the present invention that are particularly effective in inhibiting the polymerization of vinyl aromatic compounds, in particular styrene. Such compounds are N-nitroso derivatives of unsubstituted or dialkyl substituted phenylenediamines having the formula (4).

Both mono-nitroso derivatives and di-nitroso derivatives are useful as inhibitors. This compound may be used alone or in combination with phenylenediamine.

The present invention relates to a method of inhibiting polymerization of a vinyl aromatic compound during distillation. One embodiment of this method involves adding to the vinyl aromatic compound an effective amount of the reaction product of nitrous acid and an amine of formula (4).

Formula 4

In the above formula, R and R ₁ are each hydrogen or an alkyl group having 1 to 18 carbon atoms.

Another embodiment is a method of inhibiting vinyl aromatic compound polymerization in vinyl aromatic compound distillation, comprising adding to the vinyl aromatic compound an effective amount of a nitroso compound or a mixture thereof selected from the group consisting of the following formulas (1), (2) and (3). to be.

In the above formula, R and R ₁ are each hydrogen or an alkyl group having 1 to 18 carbon atoms.

Another embodiment is a method of inhibiting vinyl aromatic compound polymerization during distillation of a vinyl aromatic compound, comprising adding an effective amount of a mixture of inhibitor compounds of the formulas (1), (2) and (4) to the vinyl aromatic compound.

Formula 1

Formula 2

Formula 4

In the above formula, R and R ₁ are each hydrogen or an alkyl group having 1 to 18 carbon atoms.

The present invention relates to a method of inhibiting polymerization of a vinyl aromatic compound during distillation. Vinyl aromatic compounds to which the method of the present invention can be applied include styrene, alpha-methyl styrene, divinylbenzene, vinyl toluene, vinyl naphthalene and polyvinyl-benzene.

This method usually involves the addition of an inhibitor compound thereto while distilling off the vinyl aromatic compound. Inhibitor compounds that can be used in the method include as a nitroso compound selected from the group consisting of compounds of Formulas 1, 2, 3, or mixtures thereof.

Formula 1

N-nitroso-dialkyl phenylenediamine

Formula 2

N, N'-dinitroso-dialkylphenylene-diamine

Formula 3

N-phenyl, N'-nitroso-1,4-diamino cyclohexane

The R and R ₁ groups may each be hydrogen or an alkyl group having 1 to 18 carbon atoms. Examples of alkyl groups that can be used include methyl, ethyl, propyl, butyl, pentyl, octyl, decyl, secondary butyl, iso-butyl and isopentyl. Formulas 1 and 2 include the o, m and p isomers. Preferred compounds included in Formulas 1 and 2 are compounds of Formulas 1a and 1b.

N-nitroso-N, N'-di-3-pentyl-p-phenylenediamine

N, N'-dinitroso-N, N'-di-3-pentyl-p-phenylenediamine

Another nitroso compound which can be used as a polymerization inhibitor is N-phenyl, N'-nitroso-1,4-diamino cyclohexane of the formula (3).

Formula 3

Nitroso compounds are prepared by reacting amines with nitrous acid. The amines used to obtain these compounds have the formulas (4) and (5) below.

Formula 4

The reaction of amines with nitrous acid is known in the art and has been described fully herein. Typically, the amine reacts with nitrous acid at a temperature of -10 ° C to 10 ° C. Nitrous acid can also be produced in the reaction system by adding nitrous acid or by adding sodium nitrite and hydrochloric acid. In addition, in the case of diamine, the addition amount of nitrous acid determines whether a mononitroso compound or a dinitroso compound is obtained. However, even if nitrous acid: amine is added in a stoichiometric amount of 1: 1, a mixture of mononitroso compounds or dinitroso compounds will still be obtained. Thus, the exact nature of the reaction product will not be known. This reaction product may contain both mononitroso compounds and dinitroso compounds together with unreacted amines. In practice, unreacted amines can act as solvents for nitroso compounds.

In a preferred embodiment, the amine is N, N'-di-3-phenyl-p-phenylene-diamine represented by the following formula (4a).

The reaction product may comprise compounds 1a, 2a and 4a.

Thus, this is one embodiment of the invention using the reaction product described above as polymerization inhibitor. Alternatively, pure components can be separated and used individually or together. Each component can be separated by methods known in the art such as fractional crystallization, liquid phase chromatography and column chromatography.

In order to properly prevent the polymerization of the vinyl aromatic compound, an effective amount of the nitroso compound or a mixture thereof must be used. In the case of nitroso compounds of formulas (1) and (3), the effective amount varies from 1 to 1000 ppm by weight. If the nitroso compound has formula (2), the effective amount varies from 1 to 1000 ppm. When using mixtures of the compounds of formulas (1), (2) and (4), the amount of each component in the mixture varies as follows: 18 to 96% by weight of compound 1, 2 to 50% by weight of compound 2 and 2 to 80% by weight of compound %. The amount of mixture added to the vinyl aromatic compound varies from 1 to 1000 ppm by weight.

The reaction product of amines and nitrous acid can be used without further purification. Thus, if the amine is represented by formula (4), this reaction product may contain compounds other than the compounds of formulas (1), (2) and (4), and the amount of the reaction product added to the vinyl aromatic compound varies from 1 to 1000 ppm by weight.

After adding an effective amount of inhibitor to the vinyl aromatic compound containing mixture, the mixture was distilled to a temperature of 65 to 150 ° C. in a standard distillation column. The distillation temperature can be controlled by adjusting the pressure in the column to 1 to 53 kPa. The inhibitor can also be added to the vinyl aromatic compound in any convenient way. Typically the inhibitor is added to the distillate feed inlet in the required liquid phase periodically or continuously. In this regard, when the inhibitor is solid, it is dissolved in a suitable solvent. Examples of the solvent that can be used include toluene, benzene, ethylbenzene, xylene and the like. Preferred solvents are ethylbenzene or starting amines which can be easily separated from the purified vinyl aromatic compounds.

Example 1

For round bottom flasks, UOP No. 2.1 g of N, N'-di-3-pentyl-p-phenylenediamine indicated by 5 (product name, manufactured by UOP) was added. To this flask cooled to 0 ° C., 50 ml of a hydrochloric acid solution consisting of equal parts of water and concentrated hydrochloric acid was added. Then a solution of 0.51 g sodium nitrite in 12 ml water was added over 20 minutes. Then any excess acid was neutralized with chilled sodium hydroxide solution. The resulting mixture was poured into a separatory funnel and 100 ml of ethyl ether was added. The organic phases are combined and dried and ethyl ether is removed using a rotary evaporator. The isolated product was a dark liquid and was named sample A.

Example 2

The following test procedure was used to determine the styrene polymerization inhibition of Sample A. Five glass ampoules were filled with 5 g of styrene and 250 ppm by weight of Sample A. Four ampoules were placed in an oil bath and heated to 120 ° C. The fifth ampoule was analyzed to obtain an initial polymerization amount. After 1 hour, one ampoule was taken out and the contents were filtered to determine the polystyrene formation amount. This result is shown below. The experiment was repeated except that the amount of Sample A was changed each time, yielding 175, 125 and 75 ppm by weight. In addition, dinitro-butyl-phenol (DNBP) and dinitro-phenol (DNP) were tested in the same manner to provide the following comparative example and the results were also recorded.

Polymerization Inhibitor Activity of Various Inhibitors Sample % Polymerization rate Early 1 hours 2 hours 3 hours 4 hours Sample A (250 ppm) 0 0 0 0 0 Sample A (175 ppm) 0 0 0.3 0.1 1.3 Sample A (125 ppm) 0 0 0.5 0.1 6.3 Sample A (75 ppm) 0 0.1 0 10.3 14.2 DNBP (500 ppm) 0 0.1 0.5 1.5 - DNBP (300 ppm) 0 0 One 2 3.6 DNP (500 ppm) 0 0.2 0.5 0.8 - DNP (300 ppm) 0 0.5 0.9 1.5

The data in Table 1 shows that the inhibitors of the present invention show superior activity compared to the inhibitors of the prior art. Inhibitors of the invention exhibit the same activity as DNBP or DNP, but at a concentration of one third thereof.

The present invention is directed to adding a nitroso compound such as N-nitroso-N, N'-di-3-pentyl-p-phenylenediamine to a vinyl aromatic compound, thereby diluting the vinyl aromatic compound during the distillation of the vinyl aromatic compound. Provided are methods for inhibiting polymerization.

Claims (11)

A method of inhibiting polymerization of a compound during distillation of a vinyl aromatic compound, comprising adding a reaction product effective amount of nitrous acid and an amine having the formula (4) to the vinyl aromatic compound. Formula 4 In the above formula, R and R ₁ are each hydrogen or an alkyl group having 1 to 18 carbon atoms. The method of claim 1, wherein R and R ₁ are each selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, pentyl, secondary-butyl, iso-butyl and iso-pentyl. The method of claim 2 wherein the amine is How to be. The process of claim 1 wherein the vinyl aromatic compound is selected from the group consisting of styrene, alpha-methyl styrene, divinylbenzene, vinyl toluene, vinyl naphthalene and polyvinylbenzene. A method of inhibiting polymerization of a vinyl aromatic compound during distillation of the vinyl aromatic compound, comprising adding to the vinyl aromatic compound an effective amount of a nitroso compound selected from the group consisting of compounds of Formulas (1), (2) and (3) or mixtures thereof . Formula 1 Formula 2 Formula 3 In the above formula, R and R ₁ are each hydrogen or an alkyl group having 1 to 18 carbon atoms. The method of claim 5, wherein the nitroso compound is a mixture of a compound of formula 1 and a compound of formula 2. The method of claim 5, wherein R and R ₁ are each selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, pentyl, secondary-butyl, iso-butyl and iso-pentyl. The method of claim 5 wherein the nitroso compound is How to be. 6. The method of claim 5, wherein the nitroso compound is added as a mixture of inhibitors of formulas (1), (2) and (4). Formula 1 Formula 2 Formula 4 In the above formula, R and R ₁ are each hydrogen or an alkyl group having 1 to 18 carbon atoms. The method of claim 9, wherein the amount of the compound of formula 1 varies from 18 to 96 wt%, the amount of the compound of formula 2 varies from 2 to 50 wt%, and the amount of the compound of formula 4 varies from 2 to 80 wt% . 10. The method of claim 9, wherein compounds 1, 2 and 4 have the formulas 1a, 2a and 4a. Formula 1a Formula 2a Formula 4a